Multicast IP Routing protocols are used to distribute data to multiple recipients and are one of the packet types in Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6) that include reserved multicast address blocks in IPv4 and IPv6. Using multicast, a source client can send a single copy of data to a single multicast address, which is then distributed to an entire group of destination clients. A multicast group identifies a set of destination clients that are subscribed to receive a particular data stream, and are represented by an IP address from a well-defined range. Data sent to the IP address is forwarded to all members of the multicast group using hardware duplication of packets at network appliances along the packets' routes through a network.
A source client sends data to a multicast group by setting the destination IP address of an IP packet to a multicast group address. Any client can be a source client and send data to a multicast group. Source clients do not need to register before sending data to a group, and do not need to be members of the group themselves. Routers between the source client and the destination clients duplicate the data packets and forward multiple copies to the destination clients.